One entire wing of the building in the capital city of Abuja, which houses 400 workers, has been leveled, and there are an "undetermined" number of casualties. One UNICEF worker reported seeing scattered bodies strewn by the building. It's unclear as of yet who was responsible, but Nigeria has in recent months been plagued by assassinations and bombings from a radical Muslim group known as Boko Haram.
Update 1: The Associated Press is now reporting at least 16 people are dead and 11 others injured, but a Red Cross official believes the final tally will be higher.
Update 2: Boko Haram is claiming responsibility.